JP2783000B2 - Tantalum solid electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive paste used for a tantalum solid electrolytic capacitor.

[0002]

2. Description of the Related Art Conventional tantalum solid electrolytic capacitors are:
After molding the tantalum powder, vacuum sintering is performed to produce a sintered body.
Thereafter, an anodic oxide film layer, a manganese oxide layer, a carbon film layer, and a silver paste layer are formed, and terminals are attached and packaged to manufacture a capacitor.

In this capacitor, a silver paste layer is fixed via solder in a metal case to which a lead wire is attached.
There is a configuration in which the lead wire is hermetically sealed to the case, and a dip-type capacitor in which the lead wire is dipped in solder together with the capacitor element, pulled up, and then resin-coated. Also, a chip-type capacitor that performs resin molding after soldering the cathode part of the capacitor element to the lead frame with a conductive paste or a bare chip-type capacitor that simply immerses the cathode part in a solder bath to form a solder layer. is there.

[0004]

Conventionally, when immersed in a solder bath, the silver of the silver paste easily dissolves in the solder, and unless the working conditions are strictly controlled, the silver layer becomes thin or disappears. May be done. As a means to solve this drawback, a copper layer is also formed as a cathode layer, but solder erosion is controlled, but the tangent of loss angle and impedance characteristics do not become smaller than when silver paste is used. There was a problem.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a tantalum solid electrolytic capacitor which suppresses solder erosion and has excellent electrical characteristics. As a result of examining the cause of the increase in the impedance when the conventional copper paste was used, it was found that it could be improved by specifying the shape of the copper powder. It is the aspect ratio (the ratio of thickness to longest particle size)
There in 1 / 10-1 / 1 20, more preferably an average particle size used scaly copper powder 1 to 20 [mu] m.

[0006] Copper powders differ in shape depending on the manufacturing method, and are roughly classified into spherical copper powder formed by spraying molten copper, dendritic copper powder formed by crushing electrolytic copper, and flaky copper powder formed by stamping granular copper. There is. The average particle size and aspect ratio of the flaky copper powder can be controlled by grinding conditions and conditions for adding a grinding aid.

[0007] If the particle size of the flaky copper powder is too small, when it is made into a paste, the viscosity becomes large, making the coating operation difficult and increasing the impedance of the element. This is because the smaller the average particle size, the smaller the aspect ratio, and the smaller the scaly effect. Further, when the average particle size becomes larger than necessary, the impedance becomes larger. The average particle size is preferably in the range of 1 to 20 μm.

[0008] As the aspect ratio of the flaky copper particles decreases, the impedance increases as in the case of using dendritic copper particles. As the aspect ratio increases, the shape becomes more scaly and good results can be obtained. However, when it becomes excessive, a hole is formed in the scale particles, and the impedance increases.

The effect can be obtained even if not all of the metal particles in the conductive paste are flaky copper powder, and spherical copper powder, dendritic copper powder, silver fine powder can be mixed, or silver can be added to the surface of the flake copper powder. As a result of using a material coated with, the amount of flaky copper powder is preferably 70 to 95% by weight, and if the amount is small, the variation in impedance of the element becomes large.

In the case of using all of the flaky copper powder, there is no problem if the copper powder in the paste is sufficiently prevented from being oxidized, but if the handling is insufficient, the wettability with the solder is deteriorated and the practicality is lost. Although silver fine powder is mixed into the paste to prevent oxidation, it is necessary to form a thin silver layer on the surface of the flaky copper powder. If the amount is too large, the contact resistance increases due to solder erosion, and the impedance is likely to increase.

When the total amount of the metal powder in the solidified paste is 93% by weight or less, that is, when the amount of the resin such as epoxy is increased while maintaining the contact of the metal powder, the contact between the metal powders is reduced and the resistance is reduced. It is too large to be put to practical use.

[0012]

[Function] In a device cathode layer in various exterior forms of a tantalum solid electrolytic capacitor, a conductive paste layer mainly composed of flaky copper powder is formed on a surface portion which comes into contact with solder, so that solder is eroded during solder bonding. At the same time, it is possible to reduce the contact resistance of the junction, which has been difficult in the past, and to obtain a capacitor having a lower impedance than the conventional product.

This is governed by the contact resistance between the copper particles or between the copper particles and other metal particles. In the conventional copper paste, the particles were point-to-point, point-to-line, and surface-to-line contact, whereas in the present invention, surface-to-surface, surface-to-point, and surface-to-line contact increased, It has characteristics that low impedance can be obtained, soldering work of the element is easy, and variation in characteristic values is small.

[0014]

【Example】

(Comparative Example 1) Compression molding of tantalum powder and simultaneous diameter
Implant 0.25mm tantalum wire. Sinter this to 1.02x
A sintered body of 1.82 × 1.45mm is manufactured. Next, an oxide film layer, a manganese oxide layer, a carbon film layer, and a conductive silver paste layer which are to be dielectrics are formed to obtain the capacitor element 1. Using this capacitor element 1, an anode lead wire 5 is connected to the tantalum wire 2, a cathode lead wire 5 is joined to the conductive paste layer, and a dip-type tantalum solid electrolyte for forming an exterior resin 7 is obtained.

Example 1 A flaky copper powder having an average particle size of 15 μm and an aspect ratio of 1/20, a spherical copper powder having an average particle size of 15 μm, and a dendritic copper powder were added to the device 1 of Comparative Example 1 for 94 times.
A conductive paste consisting of parts by weight and 6 parts by weight of an epoxy resin is applied and cured by heating to form a conductive paste layer 3. The solder layer 4 is formed thereon, the cathode lead 5 is joined, and the exterior resin 7 is covered. This capacitor has a rated voltage of 10 V and a capacity of 10 μF, and the results of impedance measurement at 100 KHZ are shown in Table 1. It can be seen that the one using the flaky copper paste is excellent.

[0016]

[Table 1]

Example 2 A conductive paste layer 3 was formed on the element 1 of Comparative Example 1 by kneading flaky copper powder (94 parts by weight) and epoxy resin (6 parts by weight) having different average particle sizes. ,
A capacitor element similar to that of the first embodiment is manufactured. The impedance was measured at 100 KHZ. Table 2 shows the results.
Shown in Average particle size 1-20 μm, aspect ratio 1/10
It turns out that １／1/120 is appropriate.

[0018]

[Table 2]

(Example 3) A paste was kneaded with the metal powder shown in Table 3 for flaky copper powder having an average particle size of 15 µm and an aspect ratio of 1/20, and a capacitor element was manufactured. 1
Since the impedance at 00 KHZ is preferably 3Ω or less, the sample NO. 31, 40 and 41 are excluded.

[0020]

[Table 3]

Example 4 A flaky copper powder having an average particle size of 15 μm and an aspect ratio of 1/20 and a silver powder having an average particle size of 0.8 μm, and further a flaky copper powder having an average particle size of 15 μm and an aspect ratio of 1/20. A capacitor element was manufactured using silver coated (5%). Table 4 shows the results. Note that NO.
No. 51 hardens the copper paste in a nitrogen atmosphere with NO. 52 ~
58 was performed in air. NO. Others were good except 52, 57, 58. That is, NO. As is clear from 52, silver
If no powder is contained, the scale-like copper powder is oxidized
The wettability with the solder deteriorates,
The impedance increases. In addition, NO. From 57 and 58
Obviously, the content of silver powder is more than 15 parts by weight.
Also increase impedance due to silver solder erosion
You. Therefore, the content ratio of silver powder is more than 0 parts by weight,
It is desirable to use not more than part by weight.

[0022]

[Table 4]

Example 5 Sample No. 1 of the present invention 1,
The capacitors 3, 4, and 53 were housed in a well-known metal case, and were manufactured in the form of a cased capacitor, a resin-molded chip capacitor, and a bare chip capacitor with a solder sheath, and the impedance characteristics were measured. as a result,
It turns out that there is no problem with any exterior structure.

[0024]

As described above, according to the present invention, when a solder layer is joined on a device of a tantalum solid electrolytic capacitor, the solder erosion of the cathode layer is improved, so that there is no increase in impedance. In the work of soldering and joining the lead terminals to the element, work management such as temperature, time, and number of repetitions at the time of soldering can be greatly improved, which contributes to improvement in yield and stabilization of product characteristics.

[0025]

[Brief description of the drawings]

FIG. 1 is a sectional view of the present invention.

[Explanation of symbols]

1 ... capacitor element 3 ... conductive paste layer 4 ...
Solder layer.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01G 9/04

Claims (2)

(57) [Claims] 1. An oxide film layer, a manganese oxide layer, and a carbon film layer are sequentially coated on a tantalum sintered body, and an
A tantalum solid electrolytic capacitor comprising a conductive paste layer mainly composed of flaky copper powder having a spectrum ratio of 1/10 to 1/120 , and further covering a solder layer. 2. A according to claim 1 conductive paste, the size average particle size 1~20μm of the scaly copper powder, scaly copper powder amount of the paste solidified body in is 70-9 5 wt% tantalum Solid electrolytic capacitor.